1. Field of the Invention
The present invention relates to an electrical transmission line, and more particularly to an electrical transmission line with improved mechanical strength.
2. Description of the Related Art
Generally, an electrical transmission line is used for transmitting electricity to a destination and is made of conductive metal such as copper and aluminum. There are various kinds of electrical transmission lines, among which an electrical transmission line installed on the ground and extending to a long distance should have high mechanical strength.
Overhead transmission lines and electrical transmission lines for electric trains are such electrical transmission lines demanding high mechanical strength.
The electrical transmission line for electric trains provides electricity to an electric train through a pantagraph provided at the upper portion of the electric train. This electrical transmission line for electric trains should have high conductivity since it supplies electricity to a moving electric train. Also, the electrical transmission line for electric trains should have high tensile strength and high abrasion resistance since it extends several ten kilometers or several hundred kilometers and suffers from the friction against the pantagraph.
Most electrical transmission lines for electric trains available in the market are made of copper or aluminum material. However, an electrical transmission line made of copper or aluminum has low tensile strength and low abrasion resistance in spite of high conductivity, which causes a lot of maintenance costs. In other words, the electrical transmission line for electric trains made of copper or aluminum is easily worn out due to the friction against the pantagraph or easily bends or warps due to the low tensile strength, which results in frequent exchange or repair. In particular, since copper is expensive, in a case where an electrical transmission line for electric trains is made of copper, a production cost of the electrical transmission line for electric trains is increased.
Meanwhile, an overhead transmission line is an electrical transmission line for transmitting the electricity produced at a power generator to a far-off destination or primary substation, and the overhead transmission line is supported by pylons on the ground. This overhead transmission line includes a plurality of conductor units that take a charge of the transmission of electricity and support the transmission line. The conductor units are generally made of pure aluminum or aluminum alloy and are coupled and fixed to an external supporting structure such as a pylon to keep the strength of the overhead transmission line. Also, the conductor units play a role of transmitting the electricity generated at a power generator to a destination. However, the conductor units may be not suitably coupled to a pylon due to their weak mechanical strength.
In order to solve this problem, there has been proposed an ACSR (Aluminum Cable Steel Reinforced) overhead transmission line in which a central tension wire with strong mechanical strength is provided at the center of conductor units. The conductor units provided to the ACSR take a charge of the transmission of electricity and extends on the outer periphery of the central tension wire in a twisted pattern. Also, the central tension wire located at the center portion of the overhead transmission line generally adopts a steel core or a steel wire with strong mechanical strength to play a role of keeping the strength of the electrical transmission line while supporting the electrical transmission line.
However, the central tension wire occupies 30% or more of the entire weight and greatly deteriorates the electrical transmission capacity. In other words, the central tension wire formed with a steel core or a steel wire increases the weight of the entire overhead transmission line and also increases the sectional area of the overhead transmission line, thereby deteriorating the electrical transmission capacity of the entire overhead transmission line.